1. Field of the Invention
The present invention pertains to a method for determining the concentration of certain additives in petroleum fuels, such as detergent additives in motor gasoline, for example.
2. Background
Certain petroleum fuels, such as motor gasoline, contain additives which have detergent properties to prevent fouling of fuel injection systems of modern internal combustion engines. Detergent additives are usually formulated as concentrates made up of a mixture of specific compositions and are usually proprietary to the manufacturer. Anti-corrosion and deicing materials may also be in the additive mixture or "package". These types of additives are also usually added to bulk fuel shipments at the point of loading into transport vehicles, such as tank trucks, when such vehicles are loaded at distribution terminals. The additives are usually added to the fuel by injector devices which are controlled to inject different amounts of additive concentrate in accordance with the grade of the fuel product.
Various existing and expected future governmental regulations require certification of the amount of detergent additive in motor gasoline, for example. This regulatory certification creates a need for rapid, accurate, and uncomplicated methods for verifying the concentration of a particular additive in fuels offered for sale at service station pumps and other final distribution points.
Several methods have been developed for determining the concentration of certain additives in motor gasoline. Known methods generally depend on the detection of a particular, usually minor, component in the additive mixture which is assumed to be representative of the concentration of the additive in the fuel. My U S. Pat. 4,918,020 assigned to the assignee of the present invention pertains to a method for determining the presence of an invisible marker dye in motor gasoline which is added to the gasoline with an additive concentrate or "additive package" in the manner described above. The method of the '020 patent is attractive in that it is relatively uncomplicated, fast, accurate and requires very little equipment. However, the method described in '020 patent is not usable with motor gasolines which contain oxygenates. Since modern gasolines do or will all require the use of oxygenates, the solid-phase extraction method described in the '020 patent will not be useful for detecting the presence of detergent additive materials in such fuels.
U.S. Patent Application Ser. No. 07/825,343, filed Jan. 24, 1992, in the name of Sarkiss Zoumalan, and assigned to the assignee of the present invention, describes a method for detecting marker dye in motor gasoline which relies on the use of a gas chromatograph equipped with a selective nitrogen/phosphorous detector to separate the marker dye from other gasoline components and determine the nitrogen content of the marker dye. However, this method requires the use of relatively sophisticated and expensive equipment, and the response characteristics of the detector system and method require close monitoring.
Certain other methods have been considered including an evaporative/infrared technique which relies on the fact that the additive mixture usually contains an active nitrogen component which is active in the infrared detection range. Detection of this active nitrogen component can be related to the total additive mixture concentration in the fuel. In the described method, the fuel is evaporated under elevated temperature and vacuum conditions leaving the additive as a gummy residue. The method is relatively time consuming, requiring approximately eight and one half hours for evaporation of the fuel and analysis of the residue. Moreover, the method requires very careful dissolution of the residue using chloroform or similar solvents. Although the method has certain drawbacks, it is currently being considered by the State of California, U.S.A., as an acceptable method of gasoline-additive analysis.
The drawbacks associated with prior art methods, including those described above, have led to the development of the present invention which has numerous advantages described herein.